This is a Shared Instrumentation Grant proposal for a Coulter Series 753 dual dye laser flow cytometer/cell sorter. The proposal describes our present flow facility and identifies 4 distinct user groups that include a total of 22 people. The core user group consists of 6 investigators representing the Departments of Cell Biology, Pathology, and Microbiology at the University of New Mexico, School of Med. The corpus of this proposal describes the use of flow cytometry in: i) mononuclear phagocyte differentiation, ii) characterization of common antigens expressed on UV-induced tumors and UV-irradiated skin, iii) NK cell heterogeneity, iv) proto-oncogene expression in myelomonocytic development, v) regulation of phagocytosis and chemotaxis, vi) mechanisms of basophil degranulation, and vii) immunogenetics of the skin. In addition, there is a brief description of the Special Diagnostics Laboratory and the role it plays in providing research materials. Justification of a new flow system is based on the present over subscription of our facility, the necessity of an alternative system, and the requirements for a modern instrument.